The main focus of the present proposal is to understand the pharmacologic basis for differences in individual susceptibility to tobacco addiction and adverse health consequences of smoking. We propose to continue a program combining analytical and synthetic chemistry and clinical investigation, focusing on the metabolism, pharmacokinetics and pharmacodynamics of nicotine. Chemistry studies will include (a) developing methodology for quantitative analysis of tobacco alkaloids and metabolites and applying these methods to qualitatively and quantitatively define pathways of metabolism in humans; (b) synthesis of tobacco alkaloids and stereoisomers, metabolites and deuterium-labeled analogs for pharmacologic and metabolic studies, and (c) developing GC-MS assays for nicotine metabolites for stable isotope studies of nicotine metabolic disposition. Clinical studies will pursue the observation that habitual smokers regulate body levels of nicotine, testing the hypothesis that the rate of nicotine metabolism is an important determinant of individual differences in tobacco smoking behavior. Using stable isotope methodology, the kinetics of nicotine and cotinine and its relationship to daily intake of nicotine from smoking will be compared in various population groups. These include men and women, older and younger people, different racial groups (caucasians, blacks, hispanics and asians), and in heavy vs. light vs. nonsmokers. As different patterns of metabolism yielding different levels of active metabolites could contribute to individual differences, we will study the metabolism, disposition kinetics and pharmacologic effects of nicotine metabolites. Initially, we will study trans-3'-hydroxycotinine (3-HC); in future studies, the glucuronides of nicotine, cotinine and 3-HC as well as other metabolites. Since 3-HC is the major metabolite of nicotine, we will examine the utility of 3-HC as a biomarker of nicotine intake from tobacco. Environmental factors could affect nicotine metabolism. To begin to explore the nature of such influences, we will study the effects of phenobarbital, known to affect nicotine metabolism in animals, on nicotine and cotinine clearance as well as self-determined intake of nicotine from tobacco. We will explore the nature and mechanisms of differential tolerance to cardiovascular and metabolic effects of nicotine observed in light vs. heavy smokers. Using a computer- controlled infusion pump, we will determine quantitative parameters of tolerance to nicotine in individuals, and examine the influence of glucocorticoids on the sensitivity and development of tolerance to nicotine. To examine the hypothesis that subjective and cardiovascular consequences of nicotine are more pronounced with a rapid vs. low rate of dosing of nicotine, we will conduct a crossover study comparing the effects of cigarette smoking, transdermal nicotine (slow release) and nicotine nasal spray (rapid release). The proposed studies will clarify factors determining individual differences in tobacco consumption and effects, and may lead to more patient-specific and effective ways of treating tobacco addiction.